It's a dps loss for sure yes. Don't think it's that big of a loss, although clipping them halfway is really really quick. Everytime you use a global you could've used a lightning bolt or perhaps an earth shock/fulmination (I'm assuming you don't clip em when you can lava burst). Assuming a 6 minute fight for example, in a perfect scenario you'd only need to flame shock 12 times. If you clip em at 25 seconds instead, you'd need 15 flame shock casts, so 3 extra, which won't be a huge loss. Clipping them halfway pretty much means you lose 2 lightning bolt or earth shock/fulminations per minute which can add up, or can easily mess up your shock cd so you extend even more fulminations.
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Think that's 18.200 haste rating with the 5% spell haste buff.